In recent years, there is increasing concern about environment problems, and, with respect to the discharge of chemical substances that are possibly harmful to human health and ecosystem, standards, such as ISO, and laws, such as PRTR (pollutant release and transfer register) law, are applied and the regulations are being more strict. For dealing with such movements, recovery of a solvent volatilizing upon, e.g., concentration of a mixed liquid containing a solvent to reduce the amount of the solvent discharged has attracted attention, and, as apparatuses for solvent recovery, recently, a variety of separation apparatuses named, e.g., medium recovery apparatus (solvent recovery apparatus) have come onto the market.
These apparatuses separate a medium based on the principle of distillation under a normal pressure or a reduced pressure (a method in which a solvent is heated to its boiling point to generate saturated vapor and the saturated vapor is separated off), and diagrammatic views of the apparatuses are shown in FIG. 1 and FIG. 2. Reference numerals in the figures designate respective parts as follows: 1: distilling round-bottom flask; 2: heating bath; 3: thermometer; 4: condenser; 5: recovery receiver; 6: coolant connection port; 7: column; 8: solenoid valve; and 9: solenoid valve. FIG. 1 is a generally used simple distillation apparatus for organic solvent, in which solvent vapor formed by boiling a solvent is led to a condenser portion (cooling condenser for condensation 4) where the vapor is condensed and separated. The distillation apparatus of FIG. 2 is an apparatus which separates and purifies a mixed solvent comprising two or more solvents into the individual solvents of single component. In this apparatus, a distilling portion is filled with a solvent, distilling round-bottom flask 1 in the distilling portion is joined to a vertical fractional distillation portion (column tower 7), a condenser portion (cooling condenser for condensation 4) is joined to the upper part of the column, and a branch pipe extends from the condenser portion and is connected to recovery receiver 5. The apparatus has a design such that the branch pipe is further branched before the receiver to achieve reflux of part of the condensate to the upper part of fractional distillation column tower 7, and the recovery and reflux are controlled by solenoid valves 8, 9 and others, thus enabling fractional distillation of solvents. That is, the apparatus purifies a mixed solvent by boiling the organic solvents and appropriately switching the reflux and fractionation.
Japanese Patent Application No. Hei 4-86978 has a description about a method in which used waste liquor comprising n-butanol, butyl acetate, water, 2-butoxyethanol, and 2-hexyloxyethanol is separated by precipitation into an aqueous phase and a solvent phase of high-purity n-butanol and water, and fractionating is repeated under a reduced pressure to recover the solvents. However, in this method, fractionating is achieved by boiling the solvents.
In the above apparatuses, an organic solvent is “distilled” while boiling under a normal pressure or a reduced pressure in principle. For this reason, these apparatuses have the following drawbacks. (1) A solvent vapor pressure is utilized, and hence there is a need to heat a solvent to a temperature equal to or higher than its boiling point. Thus, heating bath 40 for distilling round-bottom flask receiver 26 must be heated to a temperature higher than the boiling point of the solvent. Therefore, when an organic solvent having a low flash point is used, constantly taking care to prevent flaming is indispensable from the viewpoint of achieving safe operations. (2) In the conventional apparatus which is not of a circulation system, the mechanisms of automating the addition of a solvent, the withdrawal of a purified solvent, and the discharge of concentrated mother liquor for continuously operating the apparatus are complicated due to the restrictions by the structure. (3) There are many problems to be solved, e.g., complicated structure of the apparatus and cumbersome operations.
The conventional solvent recovery apparatus comprises, for example, a rotary evaporator which evaporates a solvent under a reduced pressure, a condenser, and a diaphragm pump, and thus is of a system such that a solvent is recovered under a reduced pressure. In the conventional solvent recovery apparatus, when a mixed liquid comprising a solvent is evaporated to recover the solvent, the pressure of the outlet of the recovery portion is reduced using, e.g., a vacuum pump, so that the vaporized solvent moves from the distilling portion into the recovery portion and then into the recovery portion outlet.
However, when the outlet of the recovery portion is under a reduced pressure, the following problems occur. First, the boiling point of the solvent is lowered. In addition, the vacuum pump is difficult to regulate the degree of the reduced pressure, and hence the control of the moving speed of the vaporized solvent, namely, the retention time of the vaporized solvent in the recovery portion is difficult. Therefore, not only does the solvent recovery portion, for example, condenser need a high cooling ability, but also a high solvent concentration is required. Further, there is caused a problem in that a pressure reducing means, e.g., a vacuum pump sucks the vaporized solvent to cause a pump trouble, or leakage of the solvent occurs, for example, the solvent goes out of the apparatus.
Moreover, as apparatuses for use in the purpose of concentration, multi-ingredient sample concentration apparatuses of a system different from the principle of the above-mentioned apparatuses are commercially available as solvent concentration apparatuses. The solvent concentration apparatus is an apparatus in which a mixed liquid comprising a volatile liquid medium, such as a solvent, and a nonvolatile substance (e.g., multi-ingredient sample) is taken in a number of containers, and gas, such as carrier gas, is blown to the contents of all the containers to vaporize the solvent, thus concentrating all of the multi-ingredient samples in short order. This is called multi-ingredient sample concentration apparatus and commercially available. However, in such a solvent concentration apparatus, the vaporized solvent becomes solvent vapor that is released as such to air, together with the carrier gas, and hence the solvent vapor is not recovered. For this reason, a problem of the load on the environment arises and an apparatus which can recover the solvent vapor to be released is strongly desired, but there are the following technical difficulties to be overcome: 1) it is difficult to recover the blown-in carrier gas; 2) it is difficult to recover only the solvent from the dilute solvent vapor contained in the blown-in carrier gas; and 3) an automated apparatus is desired, but a specific method for overcoming the technical difficulties is not found, and hence the fabrication of the apparatus is difficult and such an apparatus has not yet been developed.
It is an object of the present invention to solve the above problems accompanying the conventional apparatuses and provide particularly a novel method and system for “separating and purifying” a solvent without a need to boil the solvent.
It is another object of the present invention to solve the above problems accompanying the conventional apparatuses and provide a novel system for “concentrating” a mixture comprising a liquid medium, such as a solvent, and a nonvolatile substance to recover the liquid medium without, discharging the liquid medium into air.